A seeded polymerization method based on a new functional monomer, 3-chloro-2-hydroxypropyl methacrylate (HPMA-Cl), was proposed for the synthesis of a new type of monodisperse porous, hydrophilic microspheres with reactive character. By applying the method, poly(3-chloro-2-hydroxypropyl methacrylate-co-ethylene dimethacrylate) (poly(HPMA-Cl-co-EDMA)) microspheres in the range of 4-7 mu m, with specific surface areas between 2 and 146 m(2)/g, were obtained. The microspheres are hydrophilic in nature due to the hydroxyl groups and are easily derivatizable due to the reactive chloropropyl moiety. Ligands in the form of small molecules carrying hydrophobic alkyl or hydrophilic ion exchanger groups were covalently attached onto the microspheres via simple and one-pot reactions via their chloropropyl functionality. Using the same functionality, click chemistry and surface-initiated atom transfer radical polymerization were also applied for the generation of triazole ring and zwitterionic molecular brushes on the microspheres, respectively. Poly(HPMA-Cl-co-EDMA) microspheres seem to be a promising hydrophilic reactive material particularly for the synthesis of ion exchanger resins and chromatographic stationary phases.